1. Field of the Invention
This invention relates to high consistency silicone rubber compositions, cured by hot air vulcanization, which have improved compression set.
2. Background Information
Various methods have been discovered for producing silicone rubber which has low compression set. For example, U.S. Pat. No. 2,803,619. issued Aug. 20, 1957, teaches a mixture of non-alkenyl polysiloxane and a vinyl-containing polysiloxane with an organo peroxide vulcanizing catalyst.
U.S. Pat. No. 3,183,205, issued May 11, 1965, teaches the use of a dialkyl peroxide curing agent in conjunction with a gum containing vinyl groups.
Another method for improving compression set is taught in U.S. Pat. No. 3,817,910, issued June 18, 1974. This method incorporates alkaline earth metal silicates in curable organopolysiloxane compositions.
Australian Pat. No. 8,436,959, issued July 24, 1985, describes a heat vulcanizable organopolysiloxane composition which contains at least 3 additives selected from organohydrogen polysiloxane, organofluoropolymer, organosiloxane containing at least one (meth)acryloxyalkyl group, and a boron compound.
After the method of improving the compression set of a silicone rubber which was cured by hot air-vulcanization was discovered, it was found that similiar compositions had been disclosed that provided for high tear strength silicone rubber, such as U.S. Pat. No. 4,539,357. issued Sept. 3, 1985, which teaches a silicon composition that cures to a silicone elastomer having a tear strength of above 100 psi. The composition comprises a blend of vinyl-containing gums, a silica reinforcing filler, a hydride cross-linking agent, and a peroxide curing catalyst.